Conventionally, there have been proposed techniques for collectively charging a plurality of serial-connected cells (lithium ion battery cells or the like) to achieve resource savings of a charging system. Such a charging scheme may result in cell overcharging due to mismatching of a balance of the cells. Thus, there has been known a shunt resistance scheme as a means for preventing such cell overcharging.
However, in some cases, such a conventional shunt resistance scheme may not prevent cell overcharging since this scheme is configured to flow a shunt current only by an operation of a switch. For example, if a cell is deteriorated due to aging, an increase in a battery voltage supplied to the cell cannot be sufficiently suppressed, which may result in overcharging of the cell. In particular, since a lifetime of a lithium ion battery cell may be shortened due to overcharging, there is a need to prevent the overcharging.